Many industries such as the telecommunication, chemical, and pharmaceutical industries require heated conduit lines for fluids used in manufacturing. The microelectronic semiconductor fabrication industry in particular involves the need for highly regulated gas transmission lines leading to and from the fabrication vessels used to process semiconductor wafers. These specialized gasses are used for processing applications such as low pressure chemical vapor deposition (LPCVD), metal organic chemical vapor deposition (MOCVD), high density chemical vapor deposition (HDCVD), atomic layer deposition (ALD) and plasma etch.
Generally speaking, gas delivery and exhaust lines used in semiconductor fabrication can include all the components which carry gas from the gas canisters or bottles, to the process chamber, and thereafter to the abatement equipment or scrubbers. These components can include for example valves, regulators, mass flow controls, pumps, elbows, tees, reducers and manifolds. Exhaust lines which carry gasses away from the process chamber can also be referred to as fore lines, or pump lines.
Gas delivery and exhaust lines are typically made from stainless steel. Supply lines can typically have a diameter of between about 0.25 and 0.75 inch, while exhaust lines can typically range from between about 1.5 and 6.0 inches.
The gasses delivered to and removed from the wafer fabrication reaction chamber often must be kept within a narrow range of temperatures, typically between about 70 degrees centigrade (70° C.) and 250° C., in order primarily to prevent condensation from occurring in supply lines, and sublimation of materials in the exhaust lines. Condensation or sublimation can cause defects in semiconductor devices, reducing production yields and increase the need for more frequent and/or difficult costly maintenance.
Depending on the application gas supply and exhaust lines can be heated to temperatures between about 70° C. and 250° C. The evolution of fabrication processes appear to likely require even higher temperatures. Heating the transmission lines to such temperatures requires the use of heaters which need to be insulated from the surrounding environment for heat control and safety purposes. The heaters typically operate around the clock. Control of the temperature of the lines is usually to within +/−10° C. of a target temperature. Heat time from room temperature to the processing temperature varies but is often about 30 minutes.
A typical CVD tool can have up to 30 or more individual gas transmission line heaters internal to the tool which can be controlled individually or in a master/slave configuration. Gas supply canisters can be located several hundred feet away and require multiple heaters along the transmission line. Similarly, exhaust lines are often many tens of feet long leading to scrubbers or other abatement equipment.
Lines can be heated using a heater blanket or mantle heater which wraps around the gas carrying component such as a pipe. Some heaters use fiberglass insulation and sowing materials that can unfortunately generate unwanted particulates that contaminate the surroundings.
Heater equipment using wire wound heater elements covered by a silicone foam rubber insulating material has been developed as disclosed in Hauschulz et al., U.S. Pat. No. 5,714,738, incorporated herein by reference. Silicone foam rubber provides a much cleaner, flexible solution and can be readily adapted to carry inexpensive mechanical thermal fuses rather than more expensive electronic temperature limit control devices.
However, existing silicone foam rubber heaters suffer from not being able to withstand temperatures beyond about 162° C. for extended periods of time without becoming brittle and flaking apart, leading to premature failure. These temperatures also exceed the functional limit for mechanical thermal fuses.
Another problem with wire wound heater elements is that their temperature can more easily overshoot a preferred target temperature. Further, the heat flux provided by the wire wound element can be less uniform or consistent between separate regions of the heater element. Foil etch heater elements have been used which can provide greater control and uniformity of the heat generated by separate regions of the energized element.
The instant invention results from efforts to provide an improved gas transmission line heater system which addresses one or more of the above problems.